System for optically analyzing a molten metal bath

ABSTRACT

A system for optically analyzing a molten metal bath wherein a high velocity gas stream is passed from a lance to the bath and is maintained coherent by a flame envelope to provide a clear sight pathway through the gas stream for sighting the molten metal bath longitudinally through the gas stream from a remote or spaced sighting point.

TECHNICAL FIELD

[0001] This invention relates generally to refining molten metal, e.g. steel, and, more particularly, to analyzing the molten metal bath during the refining.

BACKGROUND ART

[0002] Metals such as steel are typically produced and refined in a refractory lined vessel by heating charge materials such as metal bearing scrap, pig iron, ore, limestone, dolomite, etc. to a molten state and blowing oxygen into the resulting molten metal bath in order to oxidize impurities. It is not always possible to know the precise chemical composition of the charge materials prior to the start of processing. Therefore, the composition must be determined after the charge materials have become molten and thoroughly mixed. Moreover, the changing composition of the molten metal bath must be at least periodically determined so as to know the timing and quantity of additives made to the refining vessel contents. The standard method for determining the composition of a molten metal bath is to stop the production process, withdraw a small sample of material, and analyze this sample using a mass spectrometer.

[0003] Continuous on-line measurement is more desirable but the high temperature and the presence of dust, fume, and slag do not permit locating measuring devices inside the molten metal bath. Those skilled in the art have attempted to deal with these problems by using optical fibers close to the surface of the molten metal bath or using such aids as lenses, mirrors and prisms in order to pass data from the molten metal bath to an analyzer. However such arrangements are unsatisfactory because they are complicated to set up and difficult to maintain during the refining process, thus compromising the accuracy of the data gathered and compromising the integrity of the analysis based on such data.

[0004] Accordingly it is an object of this invention to provide a system for optically analyzing a molten metal bath which can be used on a continuous basis during the refining period which overcomes the problems inherent with presently available analysis systems.

SUMMARY OF THE INVENTION

[0005] The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is;

[0006] A method for optically analyzing a molten metal bath comprising:

[0007] (A) forming a coherent gas stream by passing a gas stream out from a lance and surrounding the gas stream with a flame envelope;

[0008] (B) passing the coherent gas stream to a molten metal bath;

[0009] (C) sighting longitudinally through the coherent gas stream to view the molten metal bath and obtain optical data therefrom; and

[0010] (D) passing the optical data to an analyzer.

[0011] Another aspect of the invention is:

[0012] Apparatus for optically analyzing a molten metal bath comprising:

[0013] (A) a molten metal furnace containing a molten metal bath;

[0014] (B) a lance having an ejection end for passing a coherent gas stream to the molten metal bath;

[0015] (C) a sight glass mounted on the lance aligned so as to view the molten metal bath longitudinally through the coherent gas stream to obtain optical data; and

[0016] (D) an analyzer and means for passing the optical data to the analyzer.

[0017] As used herein, the term “flame envelope” means a combusting stream around at least one other non-combusting gas stream.

[0018] As used herein, the term “coherent gas stream” means a gas stream whose diameter remains substantially constant.

[0019] As used herein, the term “molten metal bath” means the contents of a metal refining furnace comprising molten metal and which also may comprise slag.

[0020] As used herein, the term “optical data” means a value describing a characteristic of a molten metal bath which can be sensed by a receiver spaced from the molten metal bath.

[0021] As used herein, the term “longitudinally” means in line with the major axis.

[0022] As used herein, the term “sight glass” means an optically transparent material, such as sapphire or quartz, capable of providing a seal between a pressurized stream of gas in a lance and the fiber optic cable or other optical components. A light source, such as a laser, may be fitted to the sight glass to increase the energy of the molten metal bath observed through the coherent jet so as to improve the effectiveness of the analysis.

BRIEF DESCRIPTION OF THE DRAWING

[0023] The sole FIGURE is a simplified cross sectional representation of one preferred arrangement which may be used in the practice of the invention.

DETAILED DESCRIPTION

[0024] The invention will be described in detail with reference to the Drawing. Referring now to the FIGURE, there is shown molten metal furnace 10 which contains a molten metal bath comprising molten metal 4 and a slag layer 5, which may be molten or solid, above the pool of molten metal. Typically the molten metal will comprise iron or steel. The slag layer generally comprises one or more of calcium oxide, silicon dioxide, magnesium oxide, aluminum oxide and iron oxide.

[0025] Lance 1 is positioned so as to provide gas to the molten metal bath. The embodiment illustrated in the FIGURE is a preferred embodiment wherein the lance is positioned so as to provide gas to the molten metal bath in a direction perpendicular to the surface of the molten metal bath. Alternatively, the lance could be positioned through a sidewall of furnace 10 so as to provide gas angularly to the surface of the bath.

[0026] While any useful gas may be used in the gas stream provided to the bath from the lance, typically and preferably the gas is oxygen, such as commercial oxygen, or a gas mixture comprising oxygen. Other gases which may be used in the gas stream in the practice of this invention include nitrogen, argon, carbon dioxide, hydrogen, helium, steam, hydrocarbon gases, and gas mixtures comprising one or more thereof. The gas is provided from the lance at a high velocity, preferably at sonic or supersonic velocity. Generally the velocity of the gas stream 3 provided from the lance has a velocity of at least 1000 feet per second (fps) and preferably at least 1500 fps. Most preferably the gas stream has a supersonic velocity upon ejection from the lance and also has a supersonic velocity when it contacts the bath surface.

[0027] Fuel and oxidant are provided out from the lance around the gas stream and combust to form a flame envelope 2 around the gas stream 3. Preferably, as shown in the FIGURE, the flame envelope extends for the entire length of the gas stream within the furnace from the lance ejection end to the bath. The fuel used to form flame envelope 2 is preferably gaseous and may be any fuel such as methane or natural gas. The oxidant used to form flame envelope 2 may be air, oxygen-enriched air having an oxygen concentration exceeding that of air, or commercial oxygen having an oxygen concentration of at least 90 mole percent.

[0028] Flame envelope 2 serves to keep ambient gas, e.g. furnace gases, from being drawn into or entrained into gas stream 3, thereby keeping the velocity of stream 3 from significantly decreasing and keeping the diameter of gas stream 3 from significantly increasing, generally for a distance of at least 20 d where d is the diameter of the nozzle at the lance ejection end from which gas stream 3 is ejected. That is, flame envelope 2 serves to establish and maintain gas stream 3 as a coherent gas stream generally for a distance of at least 20 d. Preferably, as shown in the FIGURE, gas stream 3 is a coherent gas stream from the lance to the bath.

[0029] The gas or gas mixture passed to the bath in gas stream 3 serves to refine the molten metal by reacting with bath constituents and/or mixing the bath. Preferably, as shown in the FIGURE, the high velocity and coherent nature of gas stream 3 serves to drive gas stream 3 through slag layer 5 and deep into molten metal 4 so as to enhance the refining and/or mixing action of the gas delivered to the bath in gas stream 3. In the embodiment of the invention illustrated in the FIGURE the gas in gas stream 3 comprises oxygen which reacts with carbon in the molten metal to decarburize the molten metal, in the process forming gas bubbles 6 of carbon dioxide and/or carbon monoxide.

[0030] As has been discussed above, it is desirable at least periodically, and preferably continuously, to monitor the condition of the molten metal to determine, for example, its composition, temperature and/or the proportion of scrap that has been melted. In the practice of this invention these parameters are monitored by sighting through sight glass 9. Preferably, as shown in the FIGURE, sight glass 9 is mounted on lance 1 on the end opposite the ejection end to provide a pressure seal to prevent leakage of oxygen or other gases from the lance while providing an optically transparent view port.

[0031] The coherent nature of gas stream 3, which keeps furnace gases, fumes, particles, etc. from being entrained into gas stream 3, enables a clear line of sight to form from sight glass 9 to the molten metal bath. This enables viewing the molten metal bath by sighting longitudinally through the unobstructed pathway provided by coherent gas stream 3. This viewing enables the gathering of optical data from the bath. Data that can be gathered by viewing the molten metal through the coherent jet include temperature by way of optical pyrometry, measurement of the quantities of various elements contained in the molten metal bath and slag by way of spectroscopic analysis, and conditions of the process such as the proportion of melted scrap by analysis of the temperature trends.

[0032] The optical data is passed to an analyzer 7, such as by light guide assembly 8 which may comprise fiber optic cable or a system of lenses and mirrors. Analyzer 7 may be, for example, an optical spectrometer optical pyrometer, or a combination of these instruments. Analyzer 7 employs the data to provide measurements of temperature and composition of the molten metal bath, thereby enabling the operator to make adjustments to the amounts and timing of additional charge materials, fluxing agents, alloys, electrical energy, and reactive agents such as oxygen, to facilitate arriving at the desired endpoint of the refining process.

[0033] By observing the current temperature of the molten bath and the quantity of carbon, chromium, manganese or other elements remaining in the molten metal bath, the operator can determine when the processing of the metal has reached the conditions specified for the type of metal being produced. Further, if the quantity of certain trace elements such as copper are observed to be outside the quality limitations for the metal being produced, the operator will be able to make adjustments to bring the product into specification before the completion of processing. By knowing the proportion of scrap melted, the operator will know the appropriate time to add additional scrap to the furnace.

[0034] By the use of the invention one can obtain continuous and on-line measurement of molten metal bath properties without need for using optical fibers close to the surface of the molten metal bath or using such aids as lenses, mirrors and prisms. Although the invention has been described in detail with reference to a preferred embodiment, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims. 

1. A method for optically analyzing a molten metal bath comprising: (A) forming a coherent gas stream by passing a gas stream out from a lance and surrounding the gas stream with a flame envelope; (B) passing the coherent gas stream to a molten metal bath; (C) sighting longitudinally through the coherent gas stream to view the molten metal bath and obtain optical data therefrom; and (D) passing the optical data to an analyzer.
 2. The method of claim 1 wherein the sighting through the coherent gas stream comprises using a light source transmitting light through the coherent gas stream.
 3. The method of claim 2 wherein the light source is a laser.
 4. The method of claim 1 wherein the flame envelope extends from the lance to the molten metal bath.
 5. The method of claim 1 wherein the coherent gas stream has a supersonic velocity when it contacts the molten metal bath.
 6. The method of claim 1 wherein the coherent gas stream comprises oxygen.
 7. The method of claim 1 wherein the optical data enables the determination of the composition of the molten metal of the molten metal bath.
 8. The method of claim 1 wherein the optical data enables the determination of the temperature of the molten metal of the molten metal bath.
 9. The method of claim 1 wherein the molten metal bath comprises unmelted scrap and the optical data enables the determination of melted versus unmelted scrap in the molten metal bath.
 10. The method of claim 1 wherein the molten metal bath comprises molten metal and a slag layer above the molten metal, and wherein the coherent gas stream passes through the slag layer to the molten metal.
 11. Apparatus for optically analyzing a molten metal bath comprising: (A) a molten metal furnace containing a molten metal bath; (B) a lance having an ejection end for passing a coherent gas stream to the molten metal bath; (C) a sight glass mounted on the lance aligned so as to view the molten metal bath longitudinally though the coherent gas stream to obtain optical data; and (D) an analyzer and means for passing the optical data to the analyzer.
 12. The apparatus of claim 11 further comprising a light source for generating light for passage through the coherent gas stream.
 13. The apparatus of claim 12 wherein the light source is a laser.
 14. The apparatus of claim 11 wherein the lance is positioned so as to provide the coherent gas stream to the molten metal bath in a direction perpendicular to the surface of the molten metal-bath.
 15. The apparatus of claim 11 wherein the sight glass is positioned on the lance on the end opposite the ejection end of the lance.
 16. The apparatus of claim 11 wherein the means for passing optical data to the analyzer comprises a light guide assembly comprising optical fiber passing from the sight glass to the analyzer.
 17. The apparatus of claim 11 wherein the means for passing optical data to the analyzer comprises a light guide assembly comprising a system of lenses and mirrors.
 18. The apparatus of claim 11 wherein the analyzer comprises an optical spectrometer.
 19. The apparatus of claim 11 wherein the analyzer comprises a pyrometer. 